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Proximity sensors of various types are used in a variety of applications in which the distance to an object and, in some circumstances, the velocity of that object relative to the sensor are to be determined. This data can be provided to a processing system that analyzes the received data and determines if a safety threshold has been exceeded. If a safety threshold has been exceeded, the processor can determine if an alarm is to be set or other action taken. Proximity sensors are used, for example, in a variety of applications that can include burglar alarms, obstacle detection, and automobiles. Proximity sensors in automobiles can be used to determine the relative position and relative velocity of other automobiles or objects in the vicinity of the automobile. In an automobile system this position and velocity data may be used, for example, to adjust the velocity of the automobile while operating under cruise control, to apply a portion of the available brake energy to slow the vehicle down, or to provide an auditory or visual alarm indication to the driver.
One of the problems associated with the proximity and velocity sensors used in the systems described above is the detection of objects that are beyond a specified range and which may cause false alarms to be registered. In particular in an automobile system, the inability to discriminate objects based on range may result in a sudden application of brakes, the adjustment of speed in a cruise control system, or other sudden acceleration or deceleration of the automobile in response to the false alarm.
In addition to needing to be able to discriminate objects based on range, the sensors used in automobiles must be physically small, light weight, highly reliable, and low cost. The system requirement for these sensors are often quite stringent both in terms of the technical performance of the sensor and in the physical and economic factors as well. The more complex the sensor, the larger the parts count, and concomitantly, the higher the cost, the higher the mass, the larger the physical volume of the sensor, and the lower the reliability of the sensor.
Therefore, in would be advantageous to provide a sensor system, which is able to discriminate objects that are within a specified range, from objects that are outside of this range that meet the physical and economic requirements and is reliable.
A sensor is disclosed that is able to discriminate objects based on their range from the sensor. The sensor includes an antenna that transmits a sensor signal and, if an object is present receives a reflected signal therefrom. A pulsed oscillator provides a pulsed first signal having a first frequency and phase, and wherein the pulsed oscillator provides the pulsed first signal for a predetermined pulse duration and with a predetermined pulse repetition frequency. The pulsed oscillator provides the pulsed first signal to a first input port of a dual mode mixer that is further coupled to the antenna via a second port. The dual mode mixer transmits a portion of the pulsed first signal from the first input port to the second port and thus to the antenna to be transmitted as the sensor signal. In addition, the dual mode mixer uses a portion of the first signal to mix with the received reflected signal and provides a mixed signal as an output at a third port. Thus, the pulsed first signal provides both the signal to be transmitted as the sensor signal and the local oscillator signal for the mixer as well. The dual mode mixer provides a mixed signal output if the received reflected signal is present in the dual mode mixer concurrently with the pulsed first signal. Accordingly, an object can only be detected when the range to the object is such that the signal propagation time to and from the object is less than or equal to the predetermined pulse length of the pulsed first signal.
In addition, a phase shifter may be inserted in series between the second port of the dual mode mixer and the antenna. The phase shifter has a first phase shifter port and receives the portion of the first signal transmitted between the first port and the second port of the dual mode mixer. The phase shifter may selectively shift the phase of the transmitted portion of the first signal received from the dual mode mixer. The transmitted phase shifted first signal is provided as an output from a second phase shifter port of the phase shifter to the antenna. The antenna receives the transmitted phase shifted first signal and transmits it as the sensor signal. In the event that the object is present, the antenna receives the reflected signal that is reflected therefrom. The antenna provides the received reflected signal to the second phase shifter port of the phase shifter. The phase shifter may selectively shift the phase of the received reflected signal and provide a phase shifted reflected signal as an output from the first phase shifter port. The dual mode mixer receives the phase shifted reflected signal at the second port, wherein the dual mode mixer is configured and arranged to mix the phase shifted reflected signal with the pulsed first signal provided by the pulsed signal source. In this manner, signals may be shifted in phase such that two sensor signals and their respective reflected signal returns are orthogonal to one another, i.e., the two signals are ninety degrees out of phase with one another. Accordingly, in-phase and quadrature-phase signal components may be provided to enhance the accuracy and functionality of the sensor.
Other forms, features and aspects of the above-described methods and system are described in the detailed description that follows.